1. Field of the Invention
The present invention relates to a friction clutch configured to change a degree of engagement in response to variations of input torque.
2. Description of the Related Art
A friction clutch generally includes a clutch housing, a friction plate integrally rotating with the clutch housing, and a clutch inner provided inside of the clutch housing. The clutch inner includes a clutch boss which integrally rotates with a rotation shaft, a pressure member, and a clutch spring that presses the pressure member toward the clutch boss. A clutch plate which integrally rotates with the clutch boss and the friction plate are provided between the clutch boss and the pressure member.
In a clutch disclosed in JP 2009-68578 A, a relative position of the clutch boss (referred as a clutch member in JP 2009-68578 A) and the pressure member is changeable in a rotation direction of the rotation shaft. The clutch boss and the pressure member respectively include cam surfaces that come into contact with each other such that a force in the axial direction is generated when their relative position changes in the rotation direction.
When torque input to the clutch increases and then the rotation speed of the clutch housing and the friction plate increases, the rotation speed of the pressure member becomes higher than that of the clutch boss since the clutch boss integrally rotates with the rotation shaft. As a result, the relative position of the clutch boss and the pressure member shifts in the rotation direction. The clutch boss and the pressure member disclosed in JP 2009-68578 A are provided with the cam surfaces which come into contact with each other when the rotation speed of the pressure member becomes higher than that of the clutch boss. The cam surfaces generate the force which presses the pressure member toward the clutch boss (that is, increases the pressure force of the clutch spring) and thus increase the degree of engagement of the clutch boss and the pressure member with the friction plate. Further, the clutch boss and the pressure member disclosed in JP 2009-68578 A are also provided with cam surfaces which come into contact with each other when the rotation speed of the clutch boss becomes higher than that of the pressure member. The cam surfaces generate a force which separates the pressure member from the clutch boss (that is, decreases the pressure force of the clutch spring) and thus decrease the degree of engagement of the clutch boss and the pressure member with the friction plate.